Vehicle rear end warning and collision prevention is an important technological area in vehicle safety. The main reasons for vehicle rear end collision are: 1) insufficient travel distances between two vehicles; 2) adverse traveling environment, such as poor visibility due to rain, fog or snow; 3) emergency conditions such as punctured tire or broken axle; and 4) insufficient visibility of vehicles stalled on the way or pulled off to the road side.
In view of reasons 1), 2), and 3), an important factor contributing to collisions is the lag time in applying brakes or other contingency measures resulting from the brake reaction time of the driver. Owing to physiological limitations of human beings, the brake reaction time is about 1 s when the traveling speed is 60 km/h, and exceeds 2 s when the traveling speed is 120 km/h. The accidents due to the brake delay caused by the brake reaction time are dreadful; the driver cannot brake the vehicle effectively when the distance is in the range of 20-60 m resulting in rear end collision accidents.
The main research direction of existing technology is an active vehicle distance detection rear end collision warning and prevention system supported by the basic principle of vehicle distance detection technology, such that a present vehicle detects the objects (either moving or standing) within a certain distance in front of the present vehicle by the technologies such as ultrasonic, infrared, laser light, microwave Doppler, or video imaging and calculates its relative distance and speed so as to interpret the risk level of rear end collision, and thus, to start the warning system or automatic speed deceleration system so as to prevent or avoid the rear end collision. However, the existing technology has such problems as the blind area or the dead angle existing in distance scanning and detection, complicated system, poor reliability and high cost.